[OE-core] Yocto development with C++11 threads and gcc

[Khem Raj]

On Wednesday, August 13, 2014, Peter A. Bigot <pab at pabigot.com> wrote:

> On 08/13/2014 05:05 PM, Khem Raj wrote:
>
>> On Wed, Aug 13, 2014 at 2:36 PM, Peter A. Bigot <pab at pabigot.com> wrote:
>>
>>> In any case, Khem can you run with this?  It'd be fixed a lot better that
>>> way....
>>>
>> We do not configure target gcc with right matching cpu defaults,
>> atomic instruction strex/ldrex are only added after armv6 but defaults
>> for gcc if not specified is armv5t and hence it does not use the right
>> set as expected by libstdc++ which has been cross compiled. so while
>> you are at it and can reproduce it. Try to add
>>
>> EXTRA_OECONF += '${@bb.utils.contains("TUNE_FEATURES", "armv7a", "
>> --with-cpu=armv7-a", "", d)}'
>>
>> to gcc-target.inc and see if resulting gcc is any better
>>
>
> I had to make it:
>
> EXTRA_OECONF += '${@bb.utils.contains("TUNE_FEATURES", "armv7a",
> "--with-cpu=generic-armv7-a", "", d)}'
>
>
Sorry a typo there you   need  --with-arch

to get gcc to build but at runtime I then get:

>
> beaglebone[16]$ g++ -std=c++11 -pthread test.cc && ./a.out
> Assembler messages:
> Error: unknown cpu `generic-armv7-a'
> Error: unrecognized option -mcpu=generic-armv7-a
>
> which indicates the flag's being passed to the assembler which doesn't
> recognize it even though g++ is happy with it.  I suppose we could hack
> binutils to substitute whatever spelling it wants to see.
>
> (Also tried --with-cpu=arm7, but that generates assembler errors related
> to unsupported RM mode "bx lr").
>
> The approach bothers me, though.  Instead of explicitly changing
> gcc-target to match gcc-runtime, shouldn't it be a general rule that
> gcc-runtime not apply OE-specific target flags that aren't going to be used
> by direct invocations of the compiler outside of the OE build environment?
>  That seems a little more robust, as the default target flags may be
> changed upstream or by bbappends within OE, and having to make them match
> in gcc-runtime as well would be a headache.
>
> And would we need similar overrides for other architectures? There's
> something similar already in gcc-configure-common.inc for mips64.
>
> Peter
>
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